Ouabain-insensitive K-adenosine triphosphatase in distal nephron segments of the rabbit.

Abstract

An electrogenic H-ATPase sensitive to inhibition by N-ethylmaleimide has been reported to be present in renal distal tu- bules. In contrast to another H-ATPase (gastric H-K-ATP- ase), the renal enzyme is not stimulated by K+ and is not inhib- ited by vanadate. However, our preliminary observations indicated that a K-stimulated ATPase (K-ATPase) sensitive to inhibition by vanadate is present in renal medullary collecting duct (MCD). To localize and further characterize this renal tubular K-ATPase, we measured K-ATPase activity in eight specific segments of the rabbit nephron. K-ATPase activity was the difference in ATPase activity in the presence and absence of KCI but in the presence of ouabain (to inhibit Na-K- ATPase). ATPase activity was determined by a fluorometric microassay in which ATP hydrolysis is coupled to the oxida- tion of NADH. There was a significant K-ATPase activity (expressed as pmol * min-' * mm-') in the connecting tubule (CNT, 17.033), cortical collecting duct (CCD, 6.60.7), and MCD (8.81.7), but not in the proximal segments and the thick ascending limbs. The renal tubular K-ATPase was not only inhibited by vanadate but also by omeprazole and SCH 28080 (relatively specific inhibitors of gastric H-K-ATPase). It is concluded that K-ATPase present in the CNT, CCD, and MCD has some properties in common with gastric H-K-ATP- ase. However, the physiological role of K-ATPase in the distal nephron segments remains to be elucidated.